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296

PRACTICAL ORGANIC CHEMISTRY

PREPARATIONS Si  82.

Phenolphthaleiii.  The action of phthalic anhydride on
phenol takes place in two ways. When equal molecules of the
substance react in presence of cone, sulphuric acid, hydroxyan-
thraquinone is formed (Baeyer),

CJI

/co\

0

C0

/\
= C(1H4<       >C0IT.,OH + 11,0.

X-X       '

It is by a similar process that alizarin has been synthesised
with the object of ascertaining its constitution (see Notes on
Prep. 1 10, p. 316), When two molecules of phenol and one mole-
cule of phthalic anhydride are heated together with cone, sul-
phuric acid, then phenolphfhalein is formed (Baeyer). Its
constitution has been determined by its synthesis from phthalyl
chloride and benzene by means of the " Friedel-Crafts3 reaction"
(see Notes on Prep. 100, p. 309), Phthalyl chloride and benzene
yield in presence of A1C13 phthalophenone,

C jClo

U;CII5

=    QH.

CO

CO

Phthalophenone.

Phthalophenone is then converted successively into dinitro-,
diamino-, and, finally, by the action of nitrous acid, into clihydr-
oxyphthalophenone or phenolphthalein,
r^C(;U,                   r   C6H4N0.2

QH4-

/

0

CO

Phthalophenone.

CGTI4\/W
CO

Dinitrophthalophenone.

C6H4

r    C(iH4NIlo

^QII.NH;

cu' /

Mi1 M   \/

CO

Diuminophthalophenone.

4\/"
CO
Phenolphthalein.
An important group of colouring matters, known as the
" rhodamines," is obtained from phthalic anhydride and m-
aminophenol and its derivatives. They have a constitution similar